In modern semiconductor device applications, hundreds of individual devices may be packed onto a single small area of a semiconductor substrate. Many of these individual devices may need to be electrically isolated from one another. One method of accomplishing such isolation is to form a trenched isolation region between adjacent devices. Such trenched isolation region will generally comprise a trench or cavity formed within the substrate and be filled with an insulative material, such as silicon dioxide.
Prior art methods of forming trench structures are described with reference to FIGS. 1-4. Referring to FIG. 1, a semiconductor wafer fragment 10 is shown at a preliminary stage of a prior art processing sequence. Wafer fragment 10 comprises a semiconductive material 12 upon which is formed a layer of oxide 14, a layer of nitride 16, and a patterned layer of photoresist 18. Nitride layer 16 comprises an upper surface 17, upon which photoresist layer 18 is supported. Semiconductive material 12 commonly comprises monocrystalline silicon which is lightly doped with a conductivity enhancing dopant.
Referring to FIG. 2, patterned photoresist layer 18 is used as a mask for an etching process. During the etch, unmasked portions of nitride layer 16, oxide layer 14, and semiconductive material 12 are removed to form a trench 20 extending within the semiconductive material 12.
Referring to FIG. 3, photoresist layer 18 is removed. Subsequently, an oxide fill layer 24 is formed over nitride layer 16 and within trench 20.
Referring to FIG. 4, layer 24 is removed, generally by an abrasion technique such as chemical-mechanical polishing (CMP), inwardly to about upper surface 17 of nitride layer 16. Such polishing forms an oxide plug 26 within the semiconductor material 12.
A difficulty of polishing processes can be in stopping the polishing process at a desired level, such as at about upper surface 17. It would therefore be desirable to develop improved polishing processes, and to apply such polishing processes toward developing improved processes of forming field isolation regions.